A suspension is a device which influences ride comfort of passengers and steering of a vehicle. The suspension performs a function of absorbing impact generated from a road surface so as not to be directly transmitted to a vehicle frame or passengers and performs a function of causing a tire to sufficiently contact the road surface during sudden braking or sudden turning of the vehicle.
The suspension includes a spring which absorbs impact in a first one stroke and a damper which copes with impact after the first stroke. The damper controls the width (stroke) of expansion of the spring.
The main purpose of such a damper is to control ride comfort and to improve ground contact force through control of vehicle behavior in the vertical direction. However, since vehicle behavior in the vertical direction is greatly related to vehicle behavior in the lateral direction based on vehicle and tire dynamic characteristics, vehicle behavior in the lateral direction may be controlled using the damper.
In a situation in which a vehicle suddenly avoids an obstacle, steering (handling) of the vehicle and stability (balance) of a vehicle frame rather than ride comfort are important. In such an avoidance situation, relatively accurate control of vehicle behavior in the lateral direction is required and vehicle behavior in the lateral direction is deeply related to vehicle behavior in the vertical direction, and thus, driving performance of the vehicle in connection with behavior in the lateral direction may be further improved using a damper to control behavior in the vertical direction.
However, in case of conventional methods for controlling vehicle behavior using a damper, an influence degree of the damper on a yaw motion may not be estimated, or, since control of driving is performed only based on setting of the damper without considering that directionality of the influence on the yaw motion may be changed according to change of the roll motion, it is difficult to accurately control steering ability and stability of the vehicle and driving performance may be lowered according to driving situations.